Mast cells (MCs) have been implicated in many diseases affecting the gastrointestinal (GI) tract which do not involve IgE-dependent mechanisms. It has been suggested that MCs importantly contribute to neurogenic or complement-mediated inflammation, and to the responses initiated by the release of mediators from cells, such as eosinophils, which are recruited into sites of inflammation. But the actual roles of MCs in GI inflammatory reactions have been difficult to define. We have developed a model system to examine the role of the MC in vivo that employs normal mice, MC- deficient W/Wv mice, and W/Wv mice which have undergone local and selective reconstitution of gastric MC populations by the injection of cultured MCs derived from the bone marrow of the congenic normal (+/+) mice. These mice provide a novel method for studying GI reactions in the presence or absence of MCs, and therefore can be used to define precisely the contributions of MCs to gastric inflammatory responses. We propose to use this system to test the hypothesis that MCs importantly contribute to the plasma extravasation and leukocyte infiltration associated with gastric inflammatory responses that are elicited by substance P, C5a, or eosinophil-derived major basic protein, and that MCs influence these reactions by the production of IL-1alpha, TNF-alpha, biogenic amines and leukotrienes. We will quantify the contributions of MCs to the changes in plasma extravasation or leukocyte infiltration by assessing each reaction in normal (+/+) mice, MC-deficient W/Wv mice, and MC-reconstituted W/Wv mice. We will assess the role of TNF-alpha or IL- 1alpha by examining the expression of tissue levels of mRNA and product for these cytokines, we will identify the cells expressing the cytokines by in situ hybridization and immunohistochemical analysis, and we will test the biological importance of the cytokines by assessing the ability of anti-cytokine antibodies to inhibit the development of these reactions in vivo. We will evaluate the contribution of histamine, serotonin or leukotrienes to the changes in plasma extravasation and/or neutrophil infiltration associated with each response by examining the ability of specific mediator antagonists to inhibit the reactions. We will also assess the interdependence of changes in plasma extravasation and neutrophil accumulation by quantifying the effects of inhibiting neutrophil infiltration on the changes in plasma extravasation. We will assess the expression of adhesion molecules (P-selectin, ICAM-1 or ELAM-1) on vascular endothelial cells in these reactions, and will use anti-ICAM-1 antibodies and P-selectin "knock-out" mice to probe the roles of these structures in the reactions. Taken together, these studies will provide the first definitive assessment of the importance of the MC in each of these three inflammatory responses, and will identify some of the important MC-dependent or -independent mechanisms which relate the expression of these reactions.